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Neonicotinoid insecticides, which are the most widely used insecticides in the world, have been linked with declining populations of bees. As pollinators, bees play a critical role in ecological networks, so their loss can lead to serious knock-on effects for a wide variety of plants, and for the animals that rely on those plants for food. That includes us. Bees pollinate around a third of the plants central to the human diet, including many fruits and vegetables. While we’re at it, coffee and chocolate production also depend on healthy bee populations.

The exact mechanism by which neonicotinoid insecticides contribute to diminishing bee populations isn’t well understood. After all, the levels of neonicotinoids often used in agriculture are not immediately lethal to bees when first encountered. In other words, they don’t suddenly and dramatically die mid-air. It’s more pernicious than that. Increasing evidence shows that neonicotinoids can accumulate in individual bees and negatively effect a suite of functions including memory, flight and the ability to efficiently collect pollen. This, in turn, can be disastrous for the colony.

For example, several months ago, researchers discovered that neonicotinoid pesticides appear to impair bumblebees’ ability to vibrate during pollen collection and reduce the number of pollen grains they can collect.

 

Penelope Whitehorn at the University of Sterling in the UK and her colleagues had been studying a type of pollination mechanism that bumblebees employ, called ‘buzz pollination’. During buzz pollination, bees vibrate their flight muscles at high frequencies — in the area of 400 vibrations per second — which helps them loosen and remove sticky pollen from flowers.

Buzz pollination is a tricky skill though, and bumblebees go through what appears to be a learning process while they get the hang of it. Normally, they improve with experience.

Bumblebee covered in pollen TIM HILL VIA PIXABAY; CREATIVE COMMONS

Using sensitive microphones, the researchers analyzed the acoustic signature of bumblebees in the process of buzz pollination to better understand their behavior in the presence and absence of neonicotinoid.

“We found that control bees, who were not exposed to the pesticide, improved their pollen collection as they gained experience, which we interpreted as an ability to learn to buzz pollinate better,” said Whitehorn.

However, bumblebees exposed to neonicotinoid didn’t get better with experience. They had more difficulty generating the right vibrations and ultimately collected around 50% less pollen than the control bees. The researchers concluded that neonicotinoids might be affecting the bees’ memory and cognitive ability, which are critical for complex behaviors.

Now a new study by researchers at the University of Oulu in Finland has adds further weight to the idea that neonicotinoid exposure disrupts bee cognition.

In a new paper published in the journal The Proceedings of the Royal Society Biological Sciences, Phillip Watts, Juho Lämsä and their colleagues report an intriguing experiment.

They released individual bumblebees into a flight arena containing computer-controlled ‘robotic’ flowers that automatically registered whether a bee attempted to forage for food on the flower. The flower’s color (either yellow, orange or blue) indicated whether the flower had a desirable food available (a sugar solution) or an undesirable food (a quinine solution).  As in the wild, for a bee to learn which flowers to frequent, it had to explore, sample, and remember.

Bee arena; Juho Lämsä et al (2018) Proceedings Biol Sci 285 (1883)PHOTO (A) CREDIT: LASSI KALLEINEN; PHOTO (C) CREDIT: KARI SAIKKONEN.

Bumblebees that had been exposed to low dose imidacloprid, which is a neonicotinoid, flew as well as a control group that had not been exposed to the insecticide. The neonicotinoid-exposed group were also able to remember that yellow flowers were rewarding.

However, they appeared to have reduced foraging motivation. They were slower to begin foraging, visited fewer robotic flowers overall, and didn’t explore the variety of flowers equally. For example, the bees showed little interest in the blue flowers even before they had a chance to learn that there was no sugar to be had there.

“Avoidance of blue flowers may be interpreted as reduced foraging motivation or a reduction in ‘curiosity’ to explore a rarer flower type,” the researchers propose in the new paper.

“An implication of this result is that exposure to imidacloprid might lead to a reduced curiosity to seek novel food sources.”

The level of imidacloprid used in the study was 1 ppb (one part per billion), which is on the low end of insecticide concentrations that have been found in plant nectar near agricultural land. Indeed, much higher levels have been found on a number of crop plants. A few parts per billion may not sound like much, but it appears to be sufficient to render bees incurious.

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Is that such a problem? In a highly controlled environment, perhaps not. But out in the wild, it’s very risky to rely upon a single food source. While some bees are specialists, having evolved to depend on one particular plant species, most bees are generalists and rely instead on a variety of species. This is a survival advantage, as plants and available pollen can vary with location and time of year. Disease or environmental change can also affect plant availability, so bees that forage widely, regularly exploring potential food sources, have a better chance of contending with rapid change.

“Behavioural flexibility might allow efficient exploitation of diverse resources,” the authors explain.

“A bias caused by neonicotinoids towards avoiding exploration of potential food sources could limit resources acquisition, with possible population-level effects for bees.”

In other words, if bees don’t learn to explore, they severely limit their options. For healthy bee colonies and, by extension, global food security, we need curious bees.

Original Research:

Juho Lämsä et al (2018) Low Dose of Neonicotinoid Insecticide Reduces Foraging Motivation of Bees. Proceedings of the Royal Society Biological Sciences 285 (1883)

Curated from: Forbes.com

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